The GBT Dynamic Scheduling System: A New ...

Astronomical Data Analysis Software and Systems XVII ASP Conference Series, Vol. XXX, 2008 J. Lewis, R. Argyle, P. Bunclarck, D. Evans, and E. Gonzales-Solares, eds.

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The GBT Dynamic Scheduling System: A New Scheduling Paradigm K. ONeil, D. Balser, C. Bignell, M. Clark, J. Condon, M. McCarty, P. Marganian, A. Shelton, J. Braatz, J. Harnett, R. Maddalena, M. Mello, E. Sessoms1 National Radio Astronomy Observatories, Green Bank, WV 24944 Abstract. The Robert C. Byrd Green Bank Telescope (GBT) is implementing a new Dynamic Scheduling System (DSS) designed to maximize the observing efficiency of the telescope while ensuring that none of the flexibility and ease of use of the GBT is harmed and that the data quality of observations is not adversely affected. To accomplish this, the GBT DSS is implementing a dynamic scheduling system which schedules observers, rather than running scripts. The DSS works by breaking each project into one or more sessions which have associated observing criteria such as RA, Dec, and frequency. Potential observers may also enter dates when members of their team will not be available for either on-site or remote observing. The scheduling algorithm uses those data, along with the predicted weather, to determine the most efficient schedule for the GBT. The DSS provides all observers at least 24 hours notice of their upcoming observing. In the uncommon (< 20%) case where the actual weather does not match the predictions, a backup project, chosen from the database, is run instead. Here we give an overview of the GBT DSS project, including the ranking and scheduling algorithms for the sessions, the scheduling probabilities generation, the web framework for the system, and an overview of the results from the beta testing which were held from June – September, 2008.

1.

Introduction

The Robert C. Byrd Green Bank Telescope (GBT) spans a larger range of frequencies than other comparable centimeter/millimeter single-dish telescopes, and is located in a continental, mid-latitude region where weather is dominated by water vapor and small-scale effects. As a result, the observing efficiency of the GBT can be enhanced significantly by dynamically scheduling observations best matched to weather conditions. To date, the GBT has employed a simple form of dynamic scheduling in which two projects, one high-frequency and one low-frequency, are scheduled together in two sessions (spaced typically by two days). The high-frequency observer is allowed to choose which of the sessions he or she would like to use. The other session is used by the low-frequency observer. This scheme often results in high-frequency observers receiving little or no time if they wait for truly highfrequency weather, which compromises the ability to discharge these projects, and could delay completion of low-frequency projects if high-frequency observers 1

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Figure 1. Plots of simulated data showing the increased efficiencies which are predicted by the DSS. The plots show the observing efficiencies, a measure of how readily the observers meet the optimum telescope efficiency at a given frequency, against frequency. At left is the simulated results using the current paired-day scheduling system, at at right is the predicted efficiencies with the DSS.

choose substandard conditions to execute their observations. Additionally, not all high-frequency programs require the same weather – e.g. weather conditions which may be ideal for 18-26 Ghz observations are not necessarily the best for 50GHz observations, and vice-versa. The new Dynamic Scheduling System (DSS) allows observers to optimally match their desired weather conditions to their observations, resulting in considerably increased observing efficiency (see Figure 1). An improved scheme, and the accompanying software and hardware, for dynamically scheduling science on the GBT is required to make the most efficient use of telescope time, which is in high demand. This must be delivered however in a way which minimizes the burden on the GBT observer. These are the two primary goals of the GBT Dynamic Scheduling System (DSS). A successful implementation of the DSS should increase the average observing efficiency at high frequencies with the GBT while ensuring that the flexibility and ease of use of the GBT is fully retained, and the data quality of observations is not adversely affected. This must be accomplished with the limited FTEs available to the project (3 3.25 at any given time) and within a three year time span.

2.

How Does is Work?

Figure 2 shows the general schematic of the planned GBT DSS system. The DSS works through breaking all telescope proposals into smaller sessions, where each session contains a unique set of data which can then be scheduled on the telescope, in one or more scheduled telescope periods. An overview of the process is given below and in Figure 2. Details on the individual components can be found in Balser, D. et al (2008), Braatz, J. et al. (2008), Clark, M. et al. (2008), Harnett, J. et al(2008), Marganian, P. et al. (2008), McCarty, M. et al. (2008), and Sessoms, E. et al. (2008), all found within this volume.

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A New Scheduling Paradigm

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Figure 2. Schematic diagram showing the flow of data and information within the DSS. Blocks in red interact with the DSS but are are not components of the DSS. Blocks encased in dotted lines were tests by the beta tests run during the summer of 2008.

2.1.

Gathering Information in Advance

The first interaction the DSS has with the investigators is through gathering the data entered in the NRAO Proposal Submission Tool (PST). This provides the starting point for collecting the data needed for scheduling project sessions. The DSS database also collects pertinent information such as the proposal (and sometimes session) grades as given by the NRAO referee process. Once a proposal is accepted by the referee process for observing on the telescope, investigators can utilize the secondary (Phase II) tool to supplement and modify their proposal session information until they are satisfied with the way in which their project sessions will be scheduled on the telescope. All of these interactions happen before the proposal is considered for scheduling on the telescope (typically before the beginning of a given trimester). 2.2.

Scheduling Probabilities

Once all information on the accepted proposal is entered and validated (by the project investigators), the DSS can provide the potential observers with probabilities which indicate when the project sessions are likely to be scheduled on the telescope across a four month time period. Like all scheduling decisions made with the DSS, these probabilities are generated using the scoring, packing, and conflict resolution algorithms described in Balser, et al. (2008) and Sessoms, et al. (2008) in this volume. In this case, though, the probabilities are created using the historical weather database for the Green Bank site. These historical weather probabilities are used by the observers, the GBT support staff, and

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the DSS team to better understand when project sessions will be scheduled throughout the trimester, as well as to allow the potential observers to better plan their visit(s) to the telescope. Once the local weather forecasts become valid (3-7 days from the present), the potential observers will be given scheduling probabilities using the real weather predictions, providing a realistic look ahead for their chance of being scheduled on the telescope, and provising as much advance notice as possible for the observers. A detailed description of the scheduling probabilities is given in Clark, et al. (2008) in this volume. 2.3.

Scheduling the Telescope

Using the current weather forecasts, a 24-hour telescope schedule is created 24 hours in advance of the first observation being scheduled by the DSS scoring, packing, and scheduling. This schedule is then reviewed and modified (if necessary) by a human scheduler, and finally approved. At this point all observers associated with the scheduled project sessions are notified of the schedule. As a projects scheduled time draws near, the weather is monitored by the DSS software and the GBT telescope operator. If the weather becomes significantly worse than the predicted weather, the project may be cancelled and a back-up project which is more appropriate for the predicted weather conditions may be found. This decision is made by a GBT staff scientist and/or the observer for a given project. Additionally, if the weather becomes worse than predicted during an observing run, or if other conditions make the observing conditions worse than anticipated (e.g. significant and unexpected radio frequency intereference or problems with the instrumentation), the observer can choose to end her session early and a back-up project can be readily found to fill the remaiing time. See Harnett, et al. (2008) for more information on the scheduling process. 2.4.

Post-Observation Reports

Once a project is observed, the DSS is responsible for tracking time spent on a given project and sessions, logging all information pertinent to the various projects, and providing the statistical information needed for the variety of telescope reports required for observatory operation. This is all done through tools which mine the DSS database for information on telescope schedules, principal investigators, and observers.

3.

Underlying Software

Figure 3 shows a schematic diagrams of the componants of the DSS software as it existed for the summer, 2008 beta tests. The database was an SQL database. The higher level software is all described in Marganian, et al. (2008). Users of the system interacted primarily with the client browser, which utilized a modified version of TurboGears. Members of the DSS team also utilized the simulator tool to test the code and the underlying scoring algorithm (Balser, et al. 2008).

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Client

Server HTTP Requests

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Figure 3. Schematic software flow diagram for the GBT DSS as it existed for the beta tests run during the summer of 2008.

4.

Future Plans

Work on the new DSS for the GBT will continue for the next two years. The first full release of the software is planned for Fall, 2009. At this point the DSS will replace all scheduling software on the GBT, albeit without many of the ease-of-use features envisioned for the final product. Fall, 2010 will see a second release with significant improvements in the ease-of-use of the system as well as a number of tools which will help the referee process. Further information on the GBT DSS project can be found at http://www.gb.nrao.edu/dss. Acknowledgments. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The primary author would like to thank Maxwell James O’Ganian and William Raffi O’Ganian for all their support during the work of this project. References Balser, D. et al 2008, this volume, X Braatz, J. et al 2008, this volume, X Clark, M. et al 2008, this volume, X Harnett, J. et al 2008, this volume, X Marganian, P. et al 2008, this volume, X McCarty, M. et al 2008, this volume, X Sessoms, E. et al 2008, this volume, X

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